Many communications networks today provide high bit-rate transport over a shared medium, such as passive optical networks (PON), cable television (CATV) coaxial or hybrid fiber/coax networks, and wireless. These shared medium networks typically use time, frequency or code division multiplexing to transport data signals from a central terminal to several remote customer terminals and time division multiple access (TDMA) to transport data signals from the customer terminals to the central terminal. TDMA is characterized by non-continuous, or burst mode, data transmission.
Traditional clock and data recovery methods are generally optimized for communications systems which receive continuous data streams that have enriched spectra at the sampling frequency. In the case of non-continuous (burst mode) data transmission, the use of a very long preamble or an embedded clock is typically required to allow for data recovery when using traditional clock/data recovery methods. However, both approaches are wasteful of the link bandwidth and are not suited to making very fast (e.g., &lt;20 ns) data recovery decisions.
Other recovery methods sample a known preamble using multiple clock signals having different phases.